Exhaust system

ABSTRACT

Exhaust systems with a group of exhaust tubes wherein the group of tubes contains a torsional rotation of 180* or more. The group is covered with an outer shroud and coolant is forced to flow in the interstices between tubes.

o I United States atent [1113,631,678

Inventor Jerry L. Reed [56] References Cited China L Calif. uN1TEDSTATES PATENTS Q S- 2 1970 2,633,703 4/1953 Tenney et al. 181/60 t d J3,495,385 2/1970 Glass 60/31 a e 3,393,767 7/1968 Monk 181/67 AsslgneeThe United States of America as 2 851 853 9/1958 Quick 60,264 "Presentedby the Secretary the Navy 3,025,667 3/1962 Moorehead 239/265.252,629,455 2/1953 Cushman 181/60 EXHAUST SYSTEM 3,454,000 7/1969 Everett181/60 9 Claims, 6 Drawing Figs. FOREIGN PATENTS US. Cl 60/264, 45,1246/1935 France 60/31 60/39.5, 181/33 HC, 239/265.2 Primary ExaminerMarkM. Newman lut- Assistant Examiner warren Olsen Field of Search 60/271AttorneysR. S. Sciascia, Roy Miller and Gerald F. Baker 239/265.25ABSTRACT: Exhaust systems with a group of exhaust tubes wherein thegroup of tubes contains a torsional rotation of 180 or more. The groupis covered with an outer shroud and coolant is forced to flow in theinterstices between tubes.

ENGINE ADAPTION NOZZLE (INCLUDES TUBE INLET FAIRINGS 5 MOUN ING SLEEVE)now was 42 MANIFOLD SYSTEM PATENTED JAN M972 3.631.678

[NVEN R.

BY ROY MILLER ATTORNEY. GERALD F. BAKER AGENT.

PATENTEB m 41972 SHEET 2 [IF 4 FIG. 3.

EXHAUST SYSTEM STATEMENT OF GOVERNMENT INTEREST The invention describedherein may be manufactured and used by or for the Government of theUnited States of America for governmental purposes without the paymentof any royalties thereon or therefor.

BACKGROUND OF THE INVENTION Current technology devoted to the solutionof pasive infrared countermeasures (IRCM) for aircraft utilizingturboshaft and turbopropeller engines has been centered around the useof designs which employ a plug center body to optically mask the view ofhot metal surfaces. However, since total airflow must be preserved toavoid large total pressure losses and static pressure gradients throughthe power turbine, the plug systems usually contribute to large changesin area over the standard tailpipe. Further, systems employing a plugand plenum have the following disadvantages:

a. Large changes in area thereby causing aircraft installation problemsfor new cowlings, and airframe skin or structural modifications.

b. The plug and plenum are constructed of porous metal material whichcreates manufacturing problems and a corresponding increase in themanufacturing unit cost.

0. The use of porous metals contributes to problems of clogging in asandy and dusty environment. Clogging causes overheating of metalsurfaces with a loss in IRCM capability. Ingestion of dust also requiresthe use of complicated and costly cleaning processes before the IRCMdevice can be reu tilized.

d. The use of systems which employ plugs also have problems relating toweld strength, fatigue, poor vibration characteristics and complexity inrepair when damaged.

SUMMARY OF THE INVENTION The invention consists of a torsional flowconvective (or film )-cooled metal infrared countermeasure. This conceptconsists of a series of passages with a discrete shape (circular,square, etc.) whose interiors are used as ducts for the engine exhaustgas flow. The interior of each duct is treated with a low-reflectancecoating (in the 1.0 to 5.0 micron spectral region) thereby inducing animproved radiative heat transfer from the exhaust gases to the ductwalls. Cooling air is forced through the gaps between each duct and isused to convectively cool, or film-cool, the walls. In the case of filmcooling, portions of each section of each passage preferably containthin slits to allow the coolant air to mix with the exhaust flow in theduct boundary layer region. The summation of all duct areas isaerodynamically matched to be equivalent to the effective diffuser areaof the engine standard tailpipe.

To optically mask the hot engine parts from direct view, the tubes arerotated 180 or more about the torsional axis. This rotational helixpreferably is matched to approximate the vectoral rotation angle of theexhaust gas flow path from the face of the rear turbine. Total pressureand static pressure gradients through the tubes may be controlled toinsure optimum diffuser efficiency (including the effects of turbulentflow in each tube). Coolant air may be obtained from an auxiliaryblowing system, through the use of ram" air or by a combination thereofso that air is forced into the interstices between the tubes.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS FIG. 1 is aschematic longitudinal cross-sectional view of a typical prior artdevice;

FIG. 2 is a schematic transverse cross-sectional view of one embodimentof the invention;

FIG. 3 is a schematic transverse cross-sectional view of a secondembodiment;

FIG. 4 is a schematic view of a third embodiment;

FIG. 5 is a schematic perspective view of a fourth embodiment; and

FIG. 6 is a schematic cross-sectional view of a single tube.

DESCRIPTION OF PRIOR ART, FIG. I

The FIG. 1 sketch is a schematic cross-sectional view of a typicalturboshaft (and turbopropeller) engine E with an infrared countermeasurekit K. The system consists of a redesigned nozzle N which includes aplug-shaped inner body P and a plenum chamber C. This type of systemutilizes a constant area flow (to reduce penalties in total pressuredrop) therefore the diameter of the system is expanded well over that ofa conventional tailpipe. The increases in total presented area anddiameters over the conventional tailpipe are presented in the followingcalculations:

a. Area calculations (Tail-on aspect) 1. Area of current tailpipe= 1r(l6.0) /4-=202 in.

2. Area of total system =-1r( 24.5 /4=-47 l .5 in.

Increase in total area +471 .5=202=269 in. =l33 percent increase b.Diameter ratio =24.5 16.0 =l.531=53 percent increase in clearancediameter (D;,).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION TorsionalConcept No. 1 (FIG. 2)

This sketch is of the cross section of a system 10 which employs I00tubes 12, each with a radius r, which equal 0.1 of the original majorradius R.

Therefore:

A =Area of the major circle =41'R T =Areas of all minor circles ='n'r(n) where n=number of tubes For constant area flow,

r=0. IOR; and

Recognizing that some pressure drop will occur in the system an increasein the number of tubes is possible to offset this loss (up to acorrected flow efficiency of 0.95 The radius of the new circle, R hasbeen increased by the addition of two tubes. Therefor: R=R+2r+R+0.2R=I.2R, an increase of 20 percent; and

Area ratio =1 .2R /R =1 .44, a 44 percent increase in area.

Torsional Concept No. 2 (FIG. 3)

This is a sketch of the cross section of a second embodiment 20 whichemploys 16 tubes 22 of equal diameter. In this case the increase inradius (R-R), AR is 36 percent of the two major axes. This conceptutilizes inlet straighteners and fairings to cover the areas betweentubes. An outer shroud 26 insures that the coolant flow through the flowducts 28 between tubes would occur under constant pressure. All tubes 22are twisted at a constant dO/dl. (radians per unit of tube length).

Tubes with a constant diameter or including diffusion could be used.

Torsional Concept No. 3 (FIG. 4)

This sketch is a typical cross section of a third embodiment 30 andemploying a mixture of tubes 32, 32', ...32" with differing radii. Thetotal area for a sample configuration would consist of:

The area ratio for a UH-lD helicopter engine =263/ 203 =l .3 or a 30percent increase.

The center of this design includes a fairing 36 and all tubes couldinclude inlet fairings (not shown). Variations in critical Reynoldsnumbers occur in each tube size. Coolant air may be positively pumpedusing flow parallel to each tube wall.

Torsional Concept No. 4 (FIG. 5)

This sketch is of a four tube embodiment 40 having a convection cooledconcept. The engine outlet flow is exhausted through the inner primarytube 43 (See FIG. 6) and diffusers 44; it is rotated through 180.Coolant air arrow A is supplied through a manifold 46 into the gap 44between the inner primary tube 43 and outer shield walls 42 where itconvectively absorbs the thermal energy absorbed by the wall from thegas stream.

The system consists of (a) inner ducts 43 used as the primary tubes; (b)an outer tube wall 42; (c) exhaust diffusers l, 2, 3, 4...; (d) amanifold system 46; and (e) an engine adaptation nozzle. Engine exhaustgases pass through the inner ducts 43 and are rotated 180 or more afterwhich they are expanded through the exhaust diffusers. Ambient air ispositively pumped into the manifold system and then passes through theannulus formed by the inner and the outer walls of the tubes. The entiresystem is attached to the engine by either a separate structural supportor is cantilevered from the engine near flange. Initial engine exhaustflow is induced into the system by use of the adaptation nozzle.

ADVANTAGES AND NEW FEATURES The concept embodied in these examples hasthe following advantages over the known prior systems:

a. Reduction in packaging size The use of a multiple tubing enclosurewith high density allows the total radius to stay within the presentairframe structural and cowling limitations. For example: A UH-lD/Hhelicopter has an 18.0-inch-diameter clearance at the cowling exit;present IRCM kits require a new cowling, this concept would not requirea new cowling and could fit within this envelope. b. Improved Structuralintegrity The use of a solid metal construction (versus porous metals)will insure higher strength, better vibration and fatigue resistance andresistance to intlight loads. Weld strengths, joint stiffness, bucklingstrength and bending moment resistance will be significantly improvedover current systems. c. Ease of ManufaCturing The use of sonic formingtechniques and modern tooling procedures should provide a means tofabricate this concept at one third to one half the cast of the currentsystem. Fewer components and the reduced number of fabrication stepswill significantly lower the time and material required to produce oneof these concepts as compared with the present lRCM techniques. d.Environmental Hazards are reduced The effects of dust ingestion areeliminated for these concepts since the coolant flow passages are verylarge compared to those of porous metals.

ALTERNATIVES There are numerous alternatives to the basic concept: a.Duct shape The ducts can be square, hexagonal, tubular or of othersymmetrical geometric shape. b. Design variations Concepts 1 through 4show that the size and number of ducts can be varied based on thedesired nozzle coefficient, allowable packaging diameter, heat transfercharacteristics and other desired design parameters. What is claimed is:l. A turbine engine exhaust system comprising: a tailpipe; a pluralityof exhaust tubes in said pipe; said tubes being helically arranged insaid pipe in such manner that airspaces are formed between said tubesand said pipe; said tubes are rotated about the torsional axis at leastto mask hot engine parts; and

means forcin coolant air through said air spaces. 2. An exhaus systemaccording to claim 1 wherein mtenor surfaces of said tubes are treatedwith a low-reflectance coat- 3. An exhaust system according to claim 1wherein said tubes comprise a plurality of spaced slits allowing coolantair to mix with exhaust flow in the boundary region within the tubes.

4. An exhaust system according to claim 3 wherein interior surfaces ofsaid tubes are treated with a low-reflectance coat- 5. An exhaust systemaccording to claim 1 wherein the summation of all tube areas isacrodynamically equivalent to the effective diffuser area of adesignated engine.

6. An exhaust system according to claim 1 wherein the rotational helixof said tubes approximates the vectoral rotation angle of exhaust gasflow from a designated engine.

7. An exhaust system according to claim 6 wherein the summation of alltube areas is aerodynamically equivalent to the effective diffuser areaof a designated engine.

8. An exhaust system according to claim 6 wherein interior surfaces ofsaid tubes are treated with a low-reflectance coat- 9. An exhaust systemaccording to claim 6 wherein said tubes comprise a plurality of spacedslits allowing coolant air to mix with exhaust flow in the boundaryregion within the tubes.

1. A turbine engine exhaust system comprising: a tailpipe; a pluralityof exhaust Tubes in said pipe; said tubes being helically arranged insaid pipe in such manner that airspaces are formed between said tubesand said pipe; said tubes are rotated about the torsional axis at least180* to mask hot engine parts; and means forcing coolant air throughsaid air spaces.
 2. An exhaust system according to claim 1 whereininterior surfaces of said tubes are treated with a low-reflectancecoating.
 3. An exhaust system according to claim 1 wherein said tubescomprise a plurality of spaced slits allowing coolant air to mix withexhaust flow in the boundary region within the tubes.
 4. An exhaustsystem according to claim 3 wherein interior surfaces of said tubes aretreated with a low-reflectance coating.
 5. An exhaust system accordingto claim 1 wherein the summation of all tube areas is aerodynamicallyequivalent to the effective diffuser area of a designated engine.
 6. Anexhaust system according to claim 1 wherein the rotational helix of saidtubes approximates the vectoral rotation angle of exhaust gas flow froma designated engine.
 7. An exhaust system according to claim 6 whereinthe summation of all tube areas is aerodynamically equivalent to theeffective diffuser area of a designated engine.
 8. An exhaust systemaccording to claim 6 wherein interior surfaces of said tubes are treatedwith a low-reflectance coating.
 9. An exhaust system according to claim6 wherein said tubes comprise a plurality of spaced slits allowingcoolant air to mix with exhaust flow in the boundary region within thetubes.